Coaxial magnetron with improved thermal dissipation



y 1968 w. A. GERARD 3,383,551

COAXIAL MAGNETRON WITH IMPROVED THERMAL DISSIPA'IION Filed Feb. 8, 1965BERYLLIA 2 36 38 BERYLLIA WITNESSES BERYLL'A F165 INVENTOR William A.Gerard ATTORNEY Unite 3,383,551 COAXIAL MAGNETRON WITH IMHRQVED THERMALDISSlPATiON William A. Gerard, Horseheads, N.Y., assignor toWestinghouse Electric Corporation, Pittsburgh, Pa, :1 corporation ofPennsyivania Filed Feb. 8, 1965, Ser. No. 431,028 '7 (llaims. ((Il.315-39.77)

ABSTRAT OF THE DISCLOSURE This invention relates to electron dischargedevices and more particularly to coaxial magnetron type devices.

In the R. I. Collier and I. Feinstein US. Patent 2,854,- 603, issuedSept. 30, 1958, there is disclosed a coaxial magnetron structure whichcomprises an inner and outer resonant system. The inner resonant systemincludes a cylindrical anode together with a plurality of anode vanesradially extending inwardly therefrom. These vanes define acircumferential array of inner, or anode cavity resonators surrounding acathode. An outer cavity resonator is defined between an outer wall andthe cylindrical anode. The two systems are coupled by a circumferentialarray of uniformly spaced slots through the cylindrical anode whichconnect the outer resonant system with the anode cavity resonators. Theinner resonant system is designed to oscillate in the 1r mode, while theouter system is designed to oscillate in tl.e TE mode. The two systemsare effectively locked together by means of the coupling slots.

Such a structural arrangement overcomes many disadvantages inherent inmagnetrons of prior design. The conventional magnetron does have oneadvantage in that the anode vanes are connected directly to an externalwall on which exterior radiating heat fins may be positioned. The priorconventional magnetron provided a short thermal path from the anode vanetips to the heat radiating fins.

The coaxial magnetron, on the other hand, has a longer path forconduction of the heat from the anode vane tips to the outer or externalwall where radiating fins may be provided. This means in most coaxialmagnetrons that the heat must flow through the thin anode vanes, axiallyalong the thin anode cylinder and then along the end plate of the outercavity resonator to the outer cylindrical wall of the cavity resonatorwhere exterior radiating fins are provided and cooled by suitable meanssuch as air flow.

The main thermal rise in the coaxial magnetron occurs in the thin anodecylinder and in the vanes themselves where the cross section isrelatively small. In a coaxial TE mode cavity, circulating currents inthe cylindrical anode drive the coupling slots in phase. The vanes actas quarter wave transformers which provide a high voltage between theanode and cathode for interaction with electrons. For maximum voltage,the anode wall must be thin or short in an electrical sense. This is dueto the fact that it is desirable to have all the anode vane pairs of thesame length, both the ones including the coupling slot and the onesbetween the slots. The slots and. the cylindrical anode effectivelylengthen the alternate slot vane pairs States Patent making the voltagestepup nonuniform from vane to vane. This departure from uniformity isnot serious providing the anode wall is thin compared to the quarterwave length of the vanes. It is found that a thickness of onesixteenthof the operating wave length is a tolerable thickness. This is about.060 inch in the case of an X-band (9,000 megacycles) coaxial magnetron.This electrical requirement provides a severe limitation on removal ofheat.

It is accordingly an object of this invention to provide an improvedcoaxial magnetron structure. It is another object of this invention toprovide an improved means of conducting heat from the hot spots in acoaxial magnetron to the external wall thereof.

It is another object to provide additional cooling for a coaxialmagnetron without sacrificing electrical performance.

Briefly, the present invention provides improved heat removal means in acoaxial magnetron wherein high heat conductivity and electricallyinsulating material is provided in contact with the anode whereby heatfiow may be conducted through these high heat conductivity materials tothe pole pieces and auxiliary heat conductors may be positioned withinregions within the magnetron and do not affect the electricalcharacteristics of the magnetron.

Furthcr'objects and advantages of the invention will become apparent asthe following description proceeds and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part of the specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE 1 is a view of a coaxial magnetron partly in sectionincorporating the teachings of this invention;

FIG. 2 is a schematic view of the device shown in FIG. 1, illustratingthe magnetic circuit; and

FIG. 3 is a partial sectional view of a portion of FIG. l taken alongline III-Ill.

With reference now to the drawings, there is shown a coaxial magnetronembodying the present invention. The magnetron is comprised of a body orshell member 10 which is substantially cup-shaped. The body 10 includesan outer wall member 12 forming the outer wall of cavity resonator 30and a bottom wall member 14 forming the lower wall of the cavityresonator 30. The body member 10 is of a suitable electricallyconductive material such as copper. An upper end cover 16, also ofcopper, provides the upper wall of the cavity resonator 30.

Output energy from the magnetron is derived from the cavity resonator 30by means of suitable coupling means 13. A plurality of heat radiatingfins 13 are provided on the outer wall 12 of the cavity resonator 30 andonto which a suitable cooling medium such as air may be directed forcooling of the magnetron. An anode 20 is provided within the body member10. The anode 20 includes a cylindrical member 23 which defines theinner wall of the cavity resonator 30. The cylindrical anode portion 23is secured to the lower plate 14. The cylindrical anode portion 23 issecured to a flexible annular member 15. The outer periphery of themember 15 is secured to the end plate 16. In this manner the member 16which is of good thermal conductivity material such as copper permitsheat conduction from anode 2t? while still permitting expansion of theanode 20. The anode cylinder 20 includes a plurality of vanes 24 whichextend radially inwardly from the cylindrical portion 23. Centrallydisposed and extending through apertures in the end plate 16 and thebottom plate 14- is a cathode sleeve 26 which is provided with anelectron emissive coating 28 of a suitable material such as bariumoxide.

The magnetic circuit of the magnetron includes an. exhaust pole piece 31extending through the aperture provided in the upper plate 16. A cathodepole piece 32 extends through the bottom plate 14. Two substantallyhorseshoe magnets 34 are secured to the pole pieces 31 and 32.

The anode cylinder 23 includes a plurality of slots 21 arranged parallelto the axis of the tube and to the cathode sleeve 26 which extends fromsubstantially adjacent the end cover 16 to the bottom plate 14. Tie polepieces 31 and 32 which have apertures adapted to encompass the cathodesleeve 26 have their end portions adjacent the anode vanes 24. Thermalconductive means illustrated as a ceramic ring 36 is postioned betweenthe pole face of the exhaust pole piece 31 and the vanes 24. Inaddition, a thermal conductive means in the form of ring 38 is alsoprovided between the pole face of the cathode pole piece 32 and thevanes 24. The annular ring members 36 and 38 are of a suitableelectrically insulating and thermally conducting material such asberyllia.

It is necessary in the coaxial magnetron that an annular space beprovided between the pole pieces 31. and 32 and the anode cylinder 23.This annular spacing is necessary to provide proper coupling and currentflow through the axial slots 21 provided in the cylinder 23 to thecavity resonator 30. This has been found experimentally to be aboutthree times the width of the slots 21. By providing annular cylindricalmembers 39 and 41 of ceramic in this space and due to its dielectricconstant, a narrower annular spacing can be utilized over that utilizingsimply an evacuated region in this portion. If the space is filled witha suitable material such as beryllia, the space may be reduced to aboutequal to the width of the slots 21. In this manner, auxiliary cylinders40 and 43 of copper may be added between the ceramic cylinders 39 and 41and the pole pieces 31 and 32 to provide additional thermal conductivityfrom the anode vanes 24 to the bottom plate .14 and the top plate 16.The heat is then conducted through the external wall portion 12 to theradiating fins 13.

In this manner, the heat generated at the tips of the anode vanes 24 mayalso flow through the spacers 36 and 38 to the cylinders 43 and 40respectively then to the top plate 16 and the bottom plate 14respectively and then to the radiating fins 13.

In this manner, multiple paths are provided for conducting the heat fromthe vane tips to the exterior of the envelope. By providing the ceramicmembers 39 and 41 and the copper members 40 and 43, the temperature risein the anode cylinder 23 and, in turn, the anode vane tips may bereduced. The spacers 36 and 38 provide an alternate path for heat whichhas flowed through the vanes 24. The members 36, 38, 39 and 41 may beplaced in good thermal contact by metallizing the surfaces and brazingthe metallized surfaces to the contacting copper members 24 and 20.

While there have been shown and described What are at present consideredto be the preferred embodiments of the invention, modifications theretowill readily occur to those skilled in the art. It is not desired,therefore, that the invention be limited to the specific arrangementshown and described and it is intended to cover in the appended claimsall such modifications as fall within the true spirit and scope of theinvention.

I claim as my invention:

1. A magnetron comprising a tubular wall member, a plurality of anodevanes positioned on the inner surface of said wall member and defining acircular array of anode cavity resonators, a cathode positioned withinsaid circular array of resonators, an external cavity resonatorincluding said wall member, said wall member having slots for couplingenergy from selected ones of said anode cavity resonators to saidexternal cavity resonator, end plates and an external cylindrical wallhaving radiating heat fins provided thereon, magnetic pole piecespositioned at opposite ends of said anode vanes and adjacent thereto, afirst means of electrically insulative and thermally conductive materialin thermal contact with said anode vanes and positioned between saidanode vanes and one of said pole pieces, said first means being inthermal contact with a second means of thermally conductive andelectrically conductive material provided between said one of said polepieces and said tubular wall member, said second means in thermalcontact with one of said end plates of said external cavity resonator.

2. A magnetron comprising a cylindrical anode member of thermal andelectrical conduction material, a plurality of radially extending anodevanes of thermal and electrical conductive material secured to saidcylindrical anode member and defining a plurality of anode cavityresonators, a cathode positioned coaxially within said cylindrical anodemember, means including said cylindrical anode member defining anexternal cavity resonator, said wall member having slots for couplingenergy irom selected ones of said anode cavity resonators to saidexternal cavity resonator, said external cavity resonator having endplates and an external cylindrical wall having heat radiating finsprovided thereon, said external cavity resonator of thermally andelectrically conductive material, magnetic pole pieces positioned atopposite ends of said anode vanes and adjacent thereto, an auxiliarycylinder of a thermally and electrically conductive material providedbetween one of said pole pieces and said cylindrical anode member andmeans positioned between said cylindrical anode member and saidauxiliary cylinder of a thermally conductive and electrically insulativematerial.

3. A magnetron comprising a tubular anode of a material of high thermaland electrical conductiviiy, a plural: ity of anode vanes radiallydirected from the inner surface of said tubular anode and definingcircularly disposed anode cavity resonators, a cathode positioned withinsaid circular disposed anode cavity resonators, means including saidtubular anode defining an external cavity resonator, said wall memberhaving slots for coupling energy from selected ones of said anode cavityresonators to said external cavity resonator, said external cavityresonator having end plates and an external cylindrical wall having heatradiating fins provided thereon, magnetic pole pieces extending intoopposite ends of said tubular anode and spaced from said anode vanes toform an annular region between the outer surface of one of said polepieces and the inner surface of said tubular anode, a tubular member ofa material of high thermal and electrical conductivity positioned Withinsaid region and secured to one of said end plates and thermallyconductive and electrically insulative means for electrically insulatingsaid tubular member fnom said tubular anode and said anode vanes andproviding thermal conductivity therebetween.

4. A magnetron comprising a tubular anode of a material of high thermaland electrical conductivity, a plurality of anode vanes radiallydirected from the inner surface of said tubular anode and definingcircularly disposed anode cavity resonators, said tubular anode havingmeans for coupling energy from selected ones of said anode cavityresonators, a cathode positioned Within said circular disposed anodecavity resonators, magnetic pole pieces extending into opposite ends ofsaid tubular anode and spaced from said anode vanes to form an annularregion between the outer surface of said pole piece and the innersurface of said tubular anode, a tubular member of a material of highthermal and electrical conductivity positioned with said region andspaced from said tubular anode by thermally conductive and electricallyinsulative means.

5. A coaxial magnetron comprising a tubular anode of a material of highthermal and electrical conductivity, a plurality of anode vanes radiallydirected from the inner surface of said anode and defining circularlydisposed anode cavity resonators, a cathode positioned within saidcircular disposed anode cavity resonators, means including said tubularanode defining external cavity resonator, said wall member having slotsfor coupling energy from selected ones of said anode cavity resonatorsto said external cavity resonator, said ex'ernal ca ty resonator havingan external cylindrical wall having heat radiating fins providedthereon, end plate of high thermal and electrical conducti 'tyconnecting said tubular anode to said external cylindrical wall,magnetic pole pieces extending into opposite ends of said tubular anodeand spaced from said anode vanes to form an annular region between theouter surface of one of said pole pieces and the inner surface of saidtubular anode, a heat conductive member of a material of high thermaland electrical conductivity positioned with said region and in goodthermal contact with said end plate means and means positioned betweensaid tubular anode and said member for roviding good thermalconductivity and electrical insulation therebetween.

6. A magnetron comprising a cylindrical anode mem ber of thermal andelectrical conduction material, a plurality of radially extending anodevanes of thermal and electrical conductive material secured to saidcylindrical anode member and defining a plurality of anode cavityresonators, a cathode positioned coaxially within said cylindrical anodemember, said cylindrical anode defining an inner Wall of an externalcavity resonator, said wall member having slots for coupling energy fromselected ones of said anode cavity resonators to said external cavityresonator, said external cavity resonator having end plates and anexternal cylindrical wall having heat radiating fins provided thereon,said external cavity resonator of thermal and electrical conductivematerial, magnetic pole pieces positioned at opposite ends of said anodevanes and adjacent thereto, an auxiliary cylinder of a thermally andelectrically conductive material provided between one of said polepieces and said cylindrical anode member,

means positioned between said cylindrical anode memher and saidauxiliary cylinder of a thermal conductive and electrical insulatingmaterial and a flexible member of thermal and electrical conductivitysecuring one end of said cylindrical anode member to one of said endplates to permit expansion of said cylindrical anode member.

'7. A magnetron corn 'sing a thin walled cylindrl al anode member ofgood tl crrnal and electrical conductivity, a plurality of radiallyextending anode vanes secured to said cylindrical anode member anddefining a plurality of anode cavity resonators, a cathode positionedcoaxially within said anode, means including said anode defining anexternal cavity resonator, said Wall member having slots for couplingenergy from selected ones of said anode cavity resonators to saidexternal cavity resonator, said external cavity resonator having endplates and an external cylindrical wall having heat radiating finsprovided thereon, said external cavity resonator of thermally andelectrically conductive material, pole pieces positioned at oppositeends of said anode vanes and adjacent thereto, an auxiliary cylinder ofgood heat and electrical conductivity provided between one of said polepieces and said cylindrical anode and means positioned between saidcylindrical anode and said auxiliary cylinder of a thermally conductiveand electrically insulating material to provide an auxiliary path forconducting heat from said anode without affecting the electricalproperties of said magnetron.

References tilted UNlTED STATES PATENTS 2,850,672 9/1958 Briggs 313-47 X3,169,211 2/1965 Drexler et al 315-395 3,222,557 12/1965 Meachnm et al.31346 X HERMAN KARL SAALBACH, Primary Examiner.

SAXFlELD CHATMON, 1a., Assistant Examiner.

